Analysis of the Nonlinear Behavior of a MEMS Variable Capacitor

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Today’s wireless communication systems often require a high linearity for the RF building blocks. One of these blocks can be a tunable LC filter using MEMS variable capacitors (varicaps). In these filters, the varicaps are the largest contributors to the nonlinearity. Therefore we analyze the frequency and bias dependence of the linearity of a MEMS varicap. Our analysis shows that two high frequency tones can only generate large unwanted intermodulation products in a MEMS varicap if they are close to each other. When the tones are widely separated, the nonlinear distortion can be much smaller than for other varicaps like MOS structures or junction capacitors. When the varicap is used in an LC tank (which is building block for a filter), the linearity of that tank decreases with increasing tank quality factor. This implies there is a trade-off between the linearity of a tunable LC filter and its selectivity and loss.

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Journal: TechConnect Briefs
Volume: 1, Technical Proceedings of the 2002 International Conference on Modeling and Simulation of Microsystems
Published: April 22, 2002
Pages: 234 - 237
Industry sector: Sensors, MEMS, Electronics
Topic: MEMS & NEMS Devices, Modeling & Applications
ISBN: 0-9708275-7-1